"""Button press effect — generated by Transitions Demo.

Settings:
  Effect:   Grow
  Easing:   back_out
  Duration: 0.5s

Usage:
  attach_press_effect(my_button, base_w=160, base_h=44)
"""
import time

import customtkinter as ctk


# --- easings ---
# Each easing(t) maps t in [0, 1] (linear time) to a curve in [0, ~1].
# Pick the one that matches the feel you want — back_out overshoots
# slightly and then settles, giving a tactile "snap back" finish.

def back_out(t):
    if t >= 1:
        return 1.0
    s = 1.70158
    u = t - 1
    return 1 + (s + 1) * u ** 3 + s * u ** 2


def ease_out(t):  # used for the press-in (smooth deceleration)
    return 1 - (1 - t) ** 3


# --- tween engine ---
# Time-based, ~60 fps via Tk's after(16ms). Re-uses the host widget's
# event loop, so no threads, no extra dependencies.

class Tween:
    FRAME_MS = 16

    def __init__(self, widget, duration, easing, step, on_done=None):
        self.widget = widget
        self.duration = max(duration, 0.001)
        self.easing = easing
        self.step = step          # called every frame with eased t
        self.on_done = on_done    # called once after the final frame
        self._start = None
        self._running = False

    def start(self):
        self._start = time.perf_counter()
        self._running = True
        self._tick()
        return self

    def _tick(self):
        if not self._running:
            return
        # Linear progress 0 → 1, clamped at the end.
        t = min((time.perf_counter() - self._start) / self.duration, 1.0)
        self.step(self.easing(t))   # eased value handed to the step fn
        if t < 1.0:
            self.widget.after(self.FRAME_MS, self._tick)
        else:
            self._running = False
            if self.on_done:
                self.on_done()


# Linear interpolation between two scalars.
def lerp(a, b, t):
    return a + (b - a) * t


# --- attach press effect ---
# Wraps a button so its existing command still fires, but alongside an
# animation that grows it to 108% and snaps back with back_out.

def attach_press_effect(button, base_w=160, base_h=44, duration=0.5):
    """Wrap button command with a "Grow" press animation."""
    original = button.cget('command') or (lambda: None)

    PEAK_W = max(1, int(base_w * 1.08))
    PEAK_H = max(1, int(base_h * 1.08))

    # Phase 1: smooth grow to peak (120 ms).
    def to_peak(t):
        button.configure(
            width=int(lerp(base_w, PEAK_W, t)),
            height=int(lerp(base_h, PEAK_H, t)),
        )

    # Phase 2: settle back to base size with the chosen easing.
    def to_base(t):
        button.configure(
            width=int(lerp(PEAK_W, base_w, t)),
            height=int(lerp(PEAK_H, base_h, t)),
        )

    def on_press():
        # Chain the two tweens — phase 2 starts when phase 1 finishes.
        Tween(
            button, 0.12, ease_out, to_peak,
            on_done=lambda: Tween(
                button, duration, back_out, to_base
            ).start(),
        ).start()
        original()  # still call whatever the button was originally bound to

    button.configure(command=on_press)


# --- runnable demo ---

if __name__ == "__main__":
    ctk.set_appearance_mode("dark")
    app = ctk.CTk()
    app.geometry("400x200")
    btn = ctk.CTkButton(
        app, text="Press me", width=160, height=44,
        command=lambda: print("clicked"),
    )
    btn.place(relx=0.5, rely=0.5, anchor="center")
    attach_press_effect(btn, base_w=160, base_h=44)
    app.mainloop()